Nonprofit organizations rely on the generosity of donors to help them meet their mission statements. Billions of dollars are donated to charities each year, but few people may know that religious organizations are among the biggest beneficiaries of Americans’ charitable largesse.

According to data from the National Study of American Religious Giving and the National Study of American Jewish Giving, American households donated a median of $375 to congregations, $150 to religiously identified nonprofit organizations and $250 to secular charities in 2012. Various sources repeatedly state that those who identify as religious people are more likely to be philanthropic. That likelihood may be a byproduct of the tradition of tithing.

Instituted in ancient times, tithing is a concept of giving 10 percent of one’s personal income to a religious organization. Because donors’ income was unlike it is today, centuries ago tithes often came as donations of produce and livestock. Tithing was compulsory within traditional Jewish law and practice, and Christians adopted the practice through Old Testament teachings. Tithing is mentioned in Leviticus 27:30, Numbers 18:26, Deuteronomy 14:24, and 2 Chronicles 31:5. While the New Testament does not recommend or demand tithing and only mentions that gifts should be “in keeping with income,” some religious groups continue to embrace tithing.

Depending on the religious organization, adherents to a particular faith may be encouraged to tithe. But many religious groups now leave it up to donors’ discretion with regard to how much to give.

Givers are encouraged to see where their donations go, and it’s not without reason to ask for accounting from a church, synagogue or mosque to understand how donations are attributed. Many religious groups voluntarily publish this information in weekly bulletins.